Method of manufacturing electron tube bulbs

ABSTRACT

991,398. Discharge tubes; turret machines. RADIO CORPORATION OF AMERICA. March 23, 1964 [April 2, 1963], No. 12171/64. Headings H1D and H1J. A carbon coating is produced over desired portions of the interior surface of an electron tube envelope by burning within the envelope a carbonaceous fuel deficient in oxygen, and thereafter burning off unwanted portions by a flame over-supplied with oxygen; the method permits the carbonization of the tube to be performed as one step of the process of sealing on the exhaust tubulation. The glass bulb 12 having a dome 30 and open end 24 is rotated about its axis while being indexed from station to station of a bulb tubulating machine, at the first of which the carbon coating is deposited by the introduction through end 24 of an air/acetylene gas burner. At subsequent stations, a soft and oxidizing flame polishes cut end 24 and burns off the carbon coating thereabout; a silicone rubber wiper is inserted into the bottom of the bulb to ensure complete removal of carbon; an air/hydrogen flame burns off the carbon coating on the dome 30 and preheats the latter, while an auxiliary burner preheats the lower end of exhaust tubulation 14; a needle flame punctures a hole in dome 30 and tubulation 14 is sealed thereto; the stem 16 with electron cage assembly 18 and barium getter 28 is sealed in the end 24 of the bulb; and the latter is exhausted before tubulation 14 is tipped off. Vertical movement of the burners within the bulb is sufficiently rapid to prevent the removal of the wall coating in a spiral track.

Oct. 6, 1964 STAT/01V 0 STAT/01V E v D. D. LIST METHOD- OF MANUFACTURING ELECTRON TUBE BULBS Filed April 2, 1963 INVENTOR.

DAN/a .D. [/57 g x QWJ Arron/5r United States PatentO 3,151,377 METHGD 9F MANUFACTURRNG ELECTRON TUBE BULEii Daniel B. List, Cincinnati, Ulric, assignor to Radio Corporation of America, a corporation of Delaware Filed Apr.'2, 1963, Ser. No. 27%,056 4 Ciairns. (Cl. 29-25.1)

This invention relates to electron tubes and particularly to a method of carbonizing inside portions of the envelopes of such tubes.

Glass envelope electron tubes having a coating of carbon on portions of the inside wall of the envelope are Well known. The carbon is applied to the bulb walls as a barrier against electrons which, it is believed, may otherwise bombard the bulb walls and cause release of gases therefrom. Such gases are detrimental to the electron tubes.

For electron tubes referred to as miniature electron tubes, the envelopes generally comprise a stem or header, a test tube-like bulb having a dome and an open end, and an exhaust tubulation. In the manufacture of miniature electron tubes, a bulb sub-assembly is first fabricated comprising the bulb and the exhaust tubulation which is sealed through the dome of the bulb. The stem, having mounted thereon an assembly of electrodes referred to as a cage, is then positioned within the bulb and the stern sealed to the open end of the bulb. Thereafter, the electron tube is exhausted through the exhaust tubulation which is then tipped off.

For miniature electron tubes having carbonized bulbs, the bulbs, in the past, have been carbonized in a separate operation prior to the sealing of the tubulation to the bulb. The bulb tubulating operation is another separate operation often performed on a high speed and automatic apparatus.

It is desirable that the bulb carbonizing step be performed on the tubulating machine. The combination of tubulating and bulb carbonizing operations on one machine would reduce the handling of the bulbs, hence, reduce the cost of the carbonized bulbs. In the past, however, it was not known how safely and practically to combine the bulb carbonizing operation with the bulb tubulating operation.

Two methods have been employed for carbonizing bulbs of electron tubes. One method comprises spraying a suspension of lamp black dispersed in alcohol into the bulb, drying out the alcohol, and wiping the carbon off portions of the bulb to leave a band of carbon around the inside of the bulb. The presence of carbon either in the dome or adjacent to the open end of the bulb is undesirable.

A lamp black and alcohol suspension is highly flammable and explosive. Since the bulb tubulating apparatus employs gas fires for heating and sealing the tubulation to the bulb, the addition of the spraying step to the bulb tubulating apparatus is highly dangerous. For this reason, bulb spraying is performed on a separate apparatus which is carefully designed to prevent ignition of the spray and which is isolated from any sources of flame.

The other method of applying carbon to electron tube bulbs involves a painting or swabbing of a lamp black suspension onto the inside wall of the bulbs. An applicator of suitable absorbent material is immersed in a suspension of lamp black and alcohol and the applicator is inserted into and pressed against the side of a rotating bulb. Various attempts have heretofore been made to perform this carbonizing method on the tubulating machine. A difficulty here, however, is that the bulbs become immediately heated when placed on the tubulating machine because the chucks which engage and carry the bulbs are hot from repeated passages through the tubula- BJSLB'Z? Patented Oct. 6, 1964 tion sealing fires. It was found that repeated contacts of the carbon suspension applicator with the hot bulbs dried out the applicator making frequent replacements of the applicator necessary. Further, as the applicator dried and its absorbent qualities varied, the thickness of carbon coating applied to the inside of the bulbs also varied. As the applicator dried and lost its softness and pliancy, the applicator left uncoated areas because it no longer followed the contours of the inside of the bulbs.

Therefore, it is an object of this invention to provide a novel and improved method of carbonizing inside portions of electron tube bulbs.

A further object of this invention is to provide a new and novel method of carbonizing inside portions of electron tube bulbs, said carbonizing method being suitable for use in the presence of gas burners and being performable on hot bulbs.

Further still, an object of this invention is to provide a new and novel method whereby the bulb carbonizing and tubulating operations may be performed on the same apparatus and wherein a band of carbon of uniform thickness may be provided around the inside wall of electron tube bulbs.

According to one embodiment of this invention, the glass bulbs are held in vertical orientation, dome end up, and rotated about the longitudinal axis of the bulb.

The bulbs are indexed to successive operating stations on the tubulating machine. At one station a gas burner burning a carbon fuel is inserted into the bulb. An insufficient quantity of oxygen is supplied to the burner whereby incomplete combustion occurs and a layer of carbon is deposited on the inside wall of the bulb. A-t further stations, means, to be described, are provided for cleaning the carbon off the inside wall of the bulb adjacent the lower open end of the bulb. At a further station, an oxidizing burner having a hard and needle-like flame is inserted into the bulb and the flame played onto the inside of the dome. This flame performs the functions of burning olf and cleaning the carbon from the dome and preheating the dome to permit puncture of a hole therethrough. At subsequent stations one end of a tubulation is held in contact with the dome and a needle flame is played against the inside of the dome to puncture a hole through the dome. Air may be blown through the tubulation to maintain the hole open, and the tubulation is then sealed to the dome.

Advantages of this method are that the bulb may be heated in normal fashion, the hot bulb not interfering with the application of the carbon coating, and by controlling the supply of oxygen to the carbon producing burner, thicknesses of carbon coatings may be provided uniform from bulb to bulb, and this thickness may readily be changed.

In the drawings:

FIG. 1 is a view in perspective of an electron tube assembly prior to sealing and tip off; and

FIGS. 2-6 are side elevations partly in section of a bulb in process at different operating stations of a bulb tubulating machine which may be employed for performing the method of this invention. Portions of the bulb being operated on are broken away for greater clarity.

FIG. 1 shows an assembled electron tube prior to sealing and tipping oil. The tube comprises an envelope Iii, including a bulb 12, an exhaust tubulation 14, and a stem 16. The stem 16 has an electrode cage assembly 18 secured thereto, as by Welding of connectors extending from the cage assembly to the inner ends of the stem leads 28. Bulb 12 has a band 22 of carbon around the inside wall thereof. The stem 16. and cage assembly 18 are inserted into bulb l2 and positioned so that the open end 24 of bulb 12 extends slightly beyond the glass button 26 of stem 16 and the carbon band 22 is disposed around the cage assembly 13. Mounted on top of the cage assembly T3 is a getter 28 which extends into the dome 3% of the bulb.

The assembled electron tube is completed by sealing the open end or skirt 24 of bulb 12 to the edge of stem 16, exhausting the electron tube through tubulation l4, tipping off and sealing the tubulation 14 at approximately the point marked A on the tribulation. The getter 28 is then flashed to deposit a metallic getter material, usually barium, on the inside surface of dome 39. It is important that no carbon cover the inside surfaces of the bulb in the region of dome 33d and open end 24. The reason for this is that if the getter material reacts with carbon, the getter material then loses its gettering or gas absorbent properties, and further, flakes from the glass wall. Also, carbon interferes with the sealing of glass to glass, and if present at the base, may prevent proper hermetic sealing of the stem 16 to the open end 24 of bulb 12. If carbon is present at the top of the tube, it may prevent proper sealing of tubulation 14 to the dome 30 during the bulb tubulation operation.

Only certain stations of a bulb tubulating machine are shown for the purpose of illustrating the method described herein.

A brief description of a conventional bulb tubulating machine, however, will be given.

The conventional bulb tubulating machine comprises an indexable turret having a plurality of bulb holdingchucks mounted around the periphery of the turret. Each of the chucks has a set of jaws therein which is operable to close about a cylindrical bulb inserted into the chuck either manually or automatically. The bulbs are held in vertical orientation, with their open ends extending downward. Means are provided for intermittently rotating the chucks and the bulbs held therein about the axis of the bulbs. Operating stations are provided mounted on fixed supports around the periphery of the turret. The bulbs may be indexed into successive stations for the perforn ance of operations on the bulbs. Such operations may include heating the lower end of the bulb and cutting off the lower end of the bulb to provide bulbs of fixed length, flame polishing the cut lower end, piercing a hole through the dome to provide communication between the inside of the bulb and the tubulation, and sealing a tubulation to the dome end of a bulb.

In FIG. 2, a station designated station A of a bulb tubulating machine is shown. Prior to the bulbs appearing a station A, the lower end of the bulb is cut oil. The bulb i2 is held in vertical orientation by jaws 34. A gas burner 36 is fixedly mounted on a support 38 and positioned to extend closely adjacent the lower end of a bulb 12 indexed to a position directly over the burner. Connected to burner as is a hose it connected to a gas mixer for providing a mixture of combustible gas and air to the burner. The combustible gas is one which is rich in carbon, acetylene preferably being used. By adjusting the gas mixer (not shown), the amount of air mixed with the acetylene can be varied to control the completeness of the burning of the acetylene. By providing an amount of air insufficient to permit complete combustion of the acetylene, unburned carbon from the burner flame 42 is deposited on the inside wall of bulb 12. In short, the gas flame is deficient in oxidation, i.e., deficient in oxygen to provide complete oxidation of the gas.

The carbon coats the entire inside of bulb l2 substantially uniformly. The thickness of the coating 23 is dependent upon the completeness of combustion of the gas and the length of time the bulb is positioned over burner 36. Also, the size of carbon particles deposited on the bulb can be controlled. The more complete the combustion, the small the particle size. A trial and error process may be used to determine the best coating thickness and particle size.

Thereafter, the carbonized bulb is indexed to station B shown in FIG. 3. At station B, a burner 44' having a provides only a single needle flame.

soft and oxidizing flame is used to glaze and flame polish the cut end 24 of bulb 12. In short, the flame is oversupplied with oxygen, i.e., has more oxygen than required for complete oxidation of the gas. Additionally, the flame from burner 44 serves to burn off some of the carbon from the lower portion of the inside of bulb 12. As mentioned, carbon on the lower inside of the bulb is undesirable since it interferes with the subsequent sealing of the stem 16 to the bulb.

To insure that all the carbon is removed from the lower end of the bulb, the bulb is then indexed to station C shown in FIG. 4. At station C is a wiper assembly 5% comprising an arm 52 on which is mounted a suitable wiping material 53 such as silicone rubber. Arm 52 is slidably mounted through support 54, and means, not shown, are provided for raising and lowering arm 52 between indexes of the machine turret. Silicon rubber is temperature resistant, porous, adsorbent, and rubber-like. Over-size wipers of this material may be used to ensure good wiping contact with the inside wall of the bulbs. At this station, the bulbs are rotated as the wiper assembly is raised so that the lower inside and of each bulb 12 is wiped clean of any carbon deposit after the glazing op eration shown in FIG. 3.

T he wiped bulb is then indexed to station D shown in PEG. 5. At station D the carbon deposit in the dome 30 of the bulb is burned away and the dome is preheated for puncture of a hole therethrough. A burner 60 is provided at this station slidably mounted on a support 62 and connected with a means (not shown) for raising and lowering burner 60 between indexes of the turret. Means are also provided for disposing tubulation 14 adjacent but not in contact with the dome 39 of bulb 12, and preheating flames (not shown) are provided for softening the lower end 64 of tubulation 14 prior to scaling it to the dome.

Burner 60 is supplied through hose 66 with a hydrogen and air mixture. A suflicicnt amount of air is provided and burner 66 is constructed in a known manner oxidizing flanme 68. As shown, flame 68 is directed onto a small area of the dome for the purpose of preheating this area. Flame 68 0f burner 69 additionally performs the function of burning and thus removing the carbon from the inside of dome 30. Although the needle flame is concentrated on a small area of the dome, the flame is deflected somewhat by the wall of the dome 30, as indicated, so that the surrounding portions of the dome are heated sufliciently to cause burning and removal of the carbon deposits therefrom.

In some instances it may be desirable to clean a larger area of the dome than would be cleaned by the needle flame as by itself. In such case, burner 69 may also be provided with an aperture for producing a flame 70 disposed at an angle of 45 with respect to flame 68. Although burning the same gas mixture as flame 68,

the burner aperture for flame 70 is designed to provide a relatively soft and spread flame in comparison with the needle-like flame 6S. Bulb 12 is rotated in the station shown in FIG. 5, whereby flame 70 cleans the carbon from the entire top end of the bulb.

Flames 6% and '70 are continuously lit and as burner 66 is raised and lowered into and out of bulb 12, flame 7t tends incidentally to burn a spiral path in the bulb side wall carbon layer. However, by raising and lowering burner 66 sufliciently rapidly, this incidental burning of the carbon can be made insignificant. Burner 66 is maintained within bulb 12 a suflicient time to permit complete burning of the carbon from the bulb upper end.

Thereafter, the preheated bulb is indexed to station E shown in FIG. 6 which may be similar to the station shown in FIG. 5. Since the carbon is alreadyburned from the top end of the bulb, burner 74 at station E The flame from burner 74 punctures a hole through the preheated top end of the dome 30. Tubulation 14 is moved downwardly into contact with dome 30, and a jet of air is blown downwardly through tubulation 14 for maintaining the hole open during sealing of the tubulation to the bulb. The carbon, by the method described, has been completely removed from the dome end of the bulb and therefore does not interfere with the sealing of the tubulation to the dome.

The remaining steps in the manufacture of the tube may be the same as those heretofore practiced after sealing the tubulation to the dome. For example, the electrode cage assembly 18 on the stem 16 is now inserted into the bulb 12 from the open end 24. The end 24 is then sealed to the stem 18, the tube is exhausted through the exhaust tubulation 14, the tubulation tipped off, and the getter flashed.

What is claimed is:

1. In the method of manufacturing an electron tube having an envelope made from a bulb, the steps of:

(a) burning inside the bulb a gas flame deficient in oxygen to deposit on the interior of the bulb walls a carbon coating, and

(b) thereafter burning portions of said coating from said walls by a gas flame oversupplied with oxygen.

2. Method of automatically fabricating a carbonized and tubulated electron tube bulb comprising:

(a) incompletely burning a carbonaceous fuel within said bulb for depositing a coating of carbon on the inside wall thereof,

(b) cleaning the lower inside wall of said bulb of carbon,

() directing an oxidizing flame onto the inside of the dome of said bulb for burning the carbon from portions of said dome and for preheating an area of said dome,

(d) piercing a hole through the carbon cleaned and heated area of said dome, and

(e) sealing a tubulation to the outside of said dome and in communication with said opening.

3. Method of automatically fabricating carbonized and tubulated electron tube bulbs comprising:

(a) positioning a bulb in vertical orientation, dome end up,

(b) directing a carbon flame having a deficiency of oxygen into said bulb for depositing a coating of carbon on the inside wall thereof,

(c) rotating said bulb about its longitudinal axis,

(d) pressing a wiper against the lower inside wall of said rotating bulb to wipe the carbon therefrom, (e) directing an oxidizing flame onto the inside Wall of the dome of said bulb for burning the carbon from said dome and for preheating a small area of said dome,

(f) piercing a hole through the carbon cleaned and heated area of said dome, and

(g) sealing a tubulation to the outside of said dome and in communication with said opening.

4. Method of automatically fabricating carbonized and tubulated electron tube bulbs comprising:

(a) positioning a bulb in vertical orientation, open end down,

(b) directing a carbon fed flame having a deficiency of oxygen into said bulb for depositing a coating of carbon on the inside wall thereof,

(c) directing an oxidizing flame onto the open end of said bulb for cleaning said open end of carbon,

(d) rotating said bulb about its longitudinal axis,

(e) pressing a wiper against the lower inside wall of said rotating bulb to wipe any remaining carbon therefrom,

(f) directing an oxidizing flame onto the inside of the dome of said bulb for burning and cleaning the carbon from portions of said dome and for preheating a restricted area of said dome,

(g) piercing a hole through the cleaned and heated region of said dome, and

(h) sealing a tubulation to the outside of said dome and in communication with said opening.

No references cited. 

1. IN THE METHOD OF MANUFACTURING AN ELECTRON TUBE HAVING AN ENVELOPE MADE FROM A BULB, THE STEPS OF: (A) BURNING INSIDE THE BULB A GAS FLAME DEFICIENT IN OXYGEN TO DEPOSIT ON THE INTERIOR OF THE BULB WALLS A CARBON COATING, AND 